The troll I unmasked on another forum was 100% a troll, I will share how I found out because their systems were different to here...
We had a policy of only allowing one account per user, so we had a page which flagged up duplicate accounts on the same IP address. It wasn't totally reliable because we did have e.g. couples who were on the same site, or people at the same college or living in the same house, etc, but we did keep an eye. But when these two users were flagged it set an alarm bell ringing for me, and because I was a newly appointed moderator I was being particularly diligent. But the first user (we'll call her m) was a long-term, well-known user who had herself previously been a moderator, so the idea that she could have more than one persona was ludicrous.
Anyway I kept an eye, and then the second user (we'll call her k) announced that she was going into hospital for brain surgery. At this point she joined twitter published her details online etc so I followed her. Her account went quiet but her twitter account stayed active, and in time she went in for surgery, and a couple of days later a tweet came through from someone claiming to be her sister saying she was in a coma but that people could keep tweeting as she was going to read her tweets to her knowing how much enjoyment she gets from them. At this point I would have been suspicious even if I hadn't seen the duplicate log-in on the site.
After a few days K came out of her coma and was back on the site, posting from hospital, or so she said. Except I kept an eye on her log in's, and they changed from a company IP address to a residential one in the evenings. At this point I was 99% sure that M and K were the same person and that K's story was bullshit, but I had one way to check...
The site also had a phone system, where you could dial into a server and have actual conversations with people if you wanted. It was all fairly innocent, like a voice chat room but done over the phone. If you didn't withhold your number then it would be logged on our system, and like the IP address, would appear against usernames. M didn't know this because the phone system had been implemented after she had been a moderator. So I went on to the phone system page and found m's number, and when I clicked on it all users who had called in from that number. There was m, and k, and two other users, one of whose death had been announced by M about a year previously.
It was a mobile phone number, so there was no way that they all used that number, given they all claimed to come from different parts of the country.
At that point I then brought up the IP's for the other two users and did a comparison to see how many times they clashed. They did - many times. At that point I banned all four accounts. M sent me an email asking if I could spare K because she was so reliant on the site, but I wrote back saying no, and that she knew why.
After that one of the other mods sent me an email saying that M had been flagged up the year before when the other user had died, but because she had been a moderator they had let it go because she'd said that the family had requested to see her account as it was a suicide. 
K remained active on twitter for a good while after that. She had numerous other surgeries, gained a partner, a twin sister, etc etc. I would have a quick look every few weeks or so to see if she'd died yet. And then, one new year's day, she killed herself. I didn't actually see that bit, just a few weeks later all the condolence tweets addressed to her etc etc.
It is bloody sickening. And the worst of it is that I know m's real name, I know where she lives, where she works, and I know people who know her in RL. I have told many people but somehow I think they don't always believe it's possible. I have blocked her on all social media (she moves in some of the same circles I do) and I will never engage with her personally. She knows I know, and she has been confronted by others who I have told. But I know she tried to join the same site several times after that, so I'm guessing that she is still trolling somewhere. Here even perhaps.